1. Technical Field
This invention relates generally to optical relay systems, and more particularly to a substrate guided relay that includes an input coupler having one or more reflective surfaces configured to expand received light in at least one dimension.
2. Background Art
Substrate guided relays are devices that transmit light rays from a source to a viewer. Generally speaking, substrate guided relays are optical transfer devices having a light transporting substrate, which may manufactured from glass, fused silica, or other transparent media. The substrate directs light from an input coupler to an output coupler. The light is guided along its path by the optical transfer properties of the substrate. The output coupler then delivers the light to the viewer. In some applications, the output coupler directs the light to a viewing region that is either a projection surface or a user's eye. By way of example, one application for a substrate guided relay is that of a near-to-eye display where the substrate guided relay directs light into the pupil of a user.
Substrate guided relays generally include three basic components: an input coupler that collects and receives light from a source, a substrate that transfers the light, and an output coupler that delivers light away from the substrate. Once the input coupler collects and receives the light from a source, it delivers the light to the substrate. The substrate then delivers the light to the output coupler which directs the light in the direction preferred for observation. The substrate guided relay not only transmits the light, but can transform the light as well. For example, in many prior art substrate guided relay systems, the substrate also performs expansion of the light. This expansion helps to ensure that the resulting output “bundle” of light is larger than the input “bundle” of light. The expansion also helps to ensure that the output light is uniform and easily viewable. Where the input light is spatially encoded, as can be the case with a liquid crystal display source, a liquid crystal on silicon source, or a digital light processing source, the substrate can expand an image after it has been converted to an angularly encoded or collimated image in a variety of sizes.
While pupil expansion in the substrate works, there can be issues associated with substrate-dependent pupil expansion. First, the input couplers associated with such systems can be expensive to manufacture. Often the input coupler must be manufactured to tight tolerances and coupled to the substrate in a very precise fashion. Second, some input couplers tend to work primarily with small, collimated light beams. Larger collimated beam input can be difficult to handle in more traditional input couplers.
There is thus a need for a substrate guided relay having an input coupler capable of accommodating larger collimated beam inputs.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.